Sensitivity Analysis of Ecological Models To Soil Information

Soil information is essential to many terrestrial ecological modeling
and management activities. Polygon soil maps produced from soil surveys
are currently the major source of information on the spatial distribution
of soil properties. However, there are some major problems regarding the
use of current soil maps in geographic analysis and especially in geographical
information systems (GIS).

In the generation of soil information for geographic analysis, the area
of a soil polygon is assigned with the soil property values of the soil
type as which the soil polygon was labeled. The so-generated soil property
information inherits two types of errors of soil maps: the commission
errors and attribute errors. The commission errors occur when a minimum
mapping size was imposed during the soil map generation process due to
the map scale. Areas smaller than the minimum mapping size were "filtered"
out ( Fig.1 ).
On soil maps, areas within a soil polygon have the same soil property
values. In other words, the spatial variation of soil properties within
a soil polygon is not maintained in a GIS database. As a result, the variation
of soil property values along a transect is perceived as a step function
rather than a gradual and continuous variation ( Fig. 2 ).
Soil property maps generated from conventional soil maps inherit the exact
spatial patterns of soil polygons on soil maps ( Fig.3 ).

Zhu et
al (1996) have developed a soil inference model, SoLIM (Soil Land
Inference Model). The method employs
an expert system approach and infers soil property information under fuzzy
logic. Soil information is express as SSVs. This fuzzy
representation together with the raster data model allows the representation
of spatial gradation of soil property values ( Fig. 4).

In this project, the impact and severity of soil information derived from
soil maps and soil information derived from SoLIM on the result of hydro-ecological
models will be studied and discussed.